1. Field of the Invention
The present invention relates to a pin drift or dowel drill bit for producing an undercut, with the drill bit including a shaft and a cutting edge that is disposed asymmetrically radially beyond the shaft in a front end portion of the drill bit.
2. Description of the Prior Art
A drill bit of this general type is known from German Gebrauchsmuster 77 38 522 Millich published May 24, 19878. This known drill bit has a blunt point and a radially projecting nose that are supposed to provide for the production of an undercut.
However, in practice this type of drill bit has not proven satisfactory because the drill bit runs rather unsteadily If an undercut is to be produced in material that contains pockets which have varying degrees of hardness, the use of this known drill bit is possible to only a limited extent, because it is easily deflected, resulting in a wobbling movement, and therefore produces an unsymmetrical undercut.
Furthermore, with the heretofore known drill bit it is not easy to recognize when the undercut has been completed. As a result, either the tool is used too long, or the undercut is not made large enough, so that an unsatisfactory holding force for an introduced dowel results.
It is also known to provide guide means in the region of the inlet of the blind hole for the purpose of guiding the drill bit during production of the undercut However, this process can be utilized with only relatively short drill bits. Furthermore, this process cannot be used if the undercut must be produced at a granite pocket. In addition, the wobbling movement of the tip of the drill bit makes for an inexact undercut. Unfortunately, this is in direct contrast to the requirement for producing an as exact and reproducible undercut as possible for bore holes, so that the safety reserves that theoretically result from the undercut can be fully utilized.
It is therefore an object of the present invention to provide a drill bit of the aforementioned general type that operates reliably even where the material in which a blind hole undercut is to be produced has different hardnesses, and also where the blind holes are very deep, and with which at the same time it is possible to establish or determine when production of the undercut is completed.